Leucine-rich repeat containing G-protein-coupled receptor 4 (LGR4), also known as GPR48 and BNMD17, belongs to the leucine-rich repeat containing G-protein-coupled receptor (LGR)/G-Protein-coupled Receptor (GPR) protein family of receptor proteins that are structurally similar to glycoprotein hormone receptors. LGRs are divided into three subgroups: (1) glycoprotein hormone receptors including thyroid-stimulating hormone (TSH) receptor, follicle-stimulating hormone (FSH) receptor, and luteinizing hormone (LH) receptor; (2) relaxin receptors LGR7 and LGR8; and (3) LGR4, LGR5, and LGR6.